Friday, January 06, 2006

VNS v. Grim Reaper

Here is the scoop on unexplained deaths for patients with VNS implants:

During one of the clinical trials for VNS, some patients died. "Analysis was made of the Sudden Unexplained Death in Epilepsy (SUDEP) rate compared with the expected baseline rate. A group of 791 patients with implanted vagus nerve stimulators were followed for an average of approximately 2 years each. Among this group, 15 deaths occurred during stimulation, of which six were considered to represent SUDEP. The incidence of definite/probable SUDEP was 4.5 per 1,000 person-years, and the standardized mortality ratio was 5.3 times the baseline population rate. These mortality and unexplained death rates are comparable to those seen in recent studies of new antiepileptic medications, performed on a population of patients with severe seizures. No increased risk of mortality could be attributed to VNS."

A follow up study was done. The Sudden Unexplained Death in Epilepsy Population (SUDEP) and Standardized Mortality Ratio (SMR) was less in the second study which included more patients over a longer period of time. Summary of both studies:

Sudden Unexplained Death in Epilepsy Population
Mortality/SUDEP study to FDA (6/97) Epilepsia (2/98) Annegers, Hauser
~800 patients, ~1,400 patient years VNS SMR (5.3/1,000 yrs) and SUDEP rates(4.5/1,000 yrs) consistent with refractory epilepsy population
Two year follow-up study completed Epilepsia, AES 99 Annegers, Coan
~1,800 patients, ~3,200 patient years 30% lower SMR (3.6/1,000 yrs) Lower SUDEP rates after two years of VNS (1.7/1,000 yrs > 2 yrs vs. 5.5 < 2 Yrs)

The numbers are a bit hard to follow, but essentially, if you have epilepsy and get the device, you are no more likely to experience an unexplained death than if you have epilepsy and don't get the device. What the second study shows is that if you make it more than two years with the device, you are much less likely to have an unexplained death than if you didn't get it.

Both studies were done in the late 1990s with the model 100 device and model 100 leads. I have not been able to find any such studies using the Pulse 102 device and model 300 leads.

Annegers JF, Coan SP, Hauser WA, Leestma J, Duffell W, Tarver B. Epilepsy, Vagal Nerve Stimulation by the NCP system, mortality, and sudden, unexpected, unexplained death. Epilepsia 1998;39:206-212

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